1. Field of the Invention
The present invention relates to an input torque control system of belt-type continuously variable transmission for vehicle to control an input torque inputted in a belt-type continuously variable transmission.
2. Description of the Prior Art
A continuously variable transmission suitable for a vehicle includes a V belt-type continuously variable transmission using a V belt. Generally, in the continuously variable transmission a hydraulic pressure (hereinafter referred to as a primary pulley pressure) is supplied to a cylinder chamber of a primary pulley thereof. The primary pulley pressure is generated by regulating a line pressure as an original pressure with a shift control valve, and is increased or reduced with the shift control valve to change a groove width of the primary pulley. As a result a diameter ratio of the primary pulley to a secondary pulley is changed, thereby to continuously control a gear ratio of a vehicle such as an automobile.
The shift control valve is, for example, connected near the middle of a shift link which constitutes a mechanical feedback mechanism, and one end of the shift link is connected to a movable flange of the primary pulley while the other end is connected to a step motor of a shift actuator.
An initialization operation of the step motor is performed as needed while a vehicle is stopped, for example when an engine is started so that an occurrence of a mismatch between a command value to the step motor and an operating position of the step motor to make the shift control valve travel at a position corresponding to a desired shift command value is prevented.
According to an example of an initialization operation of the step motor in the related apparatus as described above, after the step motor is moved to a hardware limit position in one direction when an ignition switch is on, the step motor is moved back to a reference position in the other direction, and then when the initialization operation of the step motor is finished, the command value to the step motor is initialized as a reference position. Thereby, it is aimed to make a command value to the step motor to correspond to a motor operating position with high accuracy, so that an accurate shift control is performed.
In this apparatus, when the initialization operation of the step motor is performed, it is necessary to actuate the step motor from the present position thereof to the hardware limit position in one direction, and therefore, a continuously variable transmission is provided with a transmission controller having a memory unit therein capable of storing a present operating position of the step motor, a pulley ratio and the like as pulley information. Moreover, the memory unit is equipped with a backup power supply to input data, and when a power supply (ignition switch) of a vehicle is turned off, the memory unit stores the pulley information with power supplied from the backup power supply.
An example of such an apparatus is shown in Japanese Patent Laid-Open Publication No. 08-178063.